The present invention relates generally to respiratory treatment devices, and specifically to nebulizers used for administering medication to a patient through respiration.
One rapidly developing area of respiratory treatment involves the administration of aerosolized medication to patients with toxic respiratory conditions through the use of nebulizers. A significant design consideration in developing such treatment systems is the prevention of environmental contamination from toxic elements which may be exhaled by the patient during treatment. Another factor in the treatment of patients with toxic respiratory conditions is that often the medication used is itself toxic, or causes unwanted side effects, to the patient and/or to attending health care personnel.
In view of the above factors, the goal in the nebulization of such toxic medications is to optimize the delivery of the medication to the alveoli, while minimizing the deposition of the medication in the patient's airways. Research has indicated that optimum alveolar deposition depends on the size of the nebulized particles. Particle size is a function of nebulizer type, baffling, and gas pressure. Particles larger than 2 microns result in increased bronchial and decreased alveolar deposition. On the other hand, a particle size of less than 1 micron can result in nonlocalized deposition anywhere in the pulmonary tree, but in most cases, these smaller particles are exhaled without performing a therapeutic function. Thus, the preferred particle size falls in the range of 1-2 microns, with an optimal particle size being 2 microns, plus or minus 0.5 micron.
Studies of conventional nebulizers have found that some nebulizers emit smaller-sized particles (less than 1 micron), and consequently do not deliver an adequate amount of medication to the patient. On the other hand, other nebulizers deliver more medication to the patient; however these latter devices generate larger particles. There has been some concern as to the size of the particles generated by these latter nebulizers, and to the consequential increased chance of patient bronchial distress.
As an example, prior to 1979, when the first cases of acquired immune deficiency syndrome (AIDS) were reported, physicians in the United States saw fewer than 100 cases of Pneumocystis carinii pneumonia (PCP) per year. Those cases occurred in patients whose immune systems were compromised due to other factors, such as disease or surgery. During that time, PCP was a treatable and preventable disease which responded well to pentamidine isethionate (pentamidine), a liquid bronchodilator medication. However, when pentamidine is used to treat PCP in AIDS patients, the resulting toxicity of the medication and resulting side effects, such as bronchial irritation and/or severe coughing, discouraged further use of this medication.
Recent studies have shown that pentamidine can be used as a prophylaxis in AIDS patients who have a high risk of developing PCP. The pentamidine has been found to be most effective when administered to the patient through a nebulizer, rather than intravenously. Also, the nebulizer has been found to reduce contamination. However, tests of conventional nebulizers have shown that in many cases, adequate amounts of pentamidine are not reaching the alveoli, but instead are being deposited in the bronchial tubes.
Thus, there is a need for a nebulizer which consistently produces an aerosol of medication comprised of a large percentage of particles in the range of 1-2 microns, while optimizing the delivery of the medication to the patient's alveoli.